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The leaflets say that the new sewer - the Thames Tideway Tunnel - is needed to help clean up the River Thames.

Tens of millions of tonnes of untreated sewage currently overflow from London's Victorian sewers after as little as 2mm of rain.

"Population growth and the continuing loss of undeveloped land able to soak up rainfall means these overflows are increasing.

The new tunnel will tackle the overflows, leading to a cleaner, healthier river for people and wildlife".

– Thames Water leaflet.

Water bills will have to go up, they add, to help raise the £4.1 billion needed to complete the project.

Sewerage charges (which you pay as part of your overall water bill) will need to rise from current levels to pay for this work, starting in 2014 at the earliest. The maximum bill impact is estimated to be in the range of £70-£80 a year.